In the field of thermal ink jet printing, it has become a common practice to provide heater resistors on a common substrate and align these heater resistors with individual ink reservoirs and corresponding ink ejection orifices in an outer nozzle plate. These heater resistors are physically defined and electrically driven by conductive traces which are photolithographically formed on the surface of a suitable resistor layer material, such as tantalum-aluminum. These heater resistors have been traditionally isolated from the overlying ink reservoirs by highly inert dielectric materials such as silicon carbide and silicon nitride. This type of thermal ink jet printhead is described, for example, in the Hewlett Packard Journal, Vol. 36, No. 5, May 1985, incorporated herein by reference.
Thus, the current flowing in this type of printhead flows laterally in the conductive trace material and then down and again laterally through the resistive tantalum aluminum layer where no trace material appears and then back up and again laterally through the conductive trace material.